Such an overcurrent release device is disclosed already in the German Patent 36 37 275. That known overcurrent release device is intrinsically safe up to seven times the rated current for the switchgear. For motor protection, however, overcurrent release devices with magnetic response levels up to twenty times the rated current are required, which results in an unprotected range between seven times the rated current and the desired response level of the magnetic release trip in the known overcurrent release device.
From the laid-open German Patent Application DE-OS 19629062 it is moreover known in an improvement of the aforementioned overcurrent release device to hold the armature in a cold state by means of an additional bimetal up to roughly ten times the rated current in the sense of response prevention and to overcome this bimetal mechanically by the magnetic force only at higher currents. When in that known overcurrent release device a current flows in the order between seven and ten times the rated current, i.e. up to the magnetic holding current, a rapid deflection of the bimetal occurs and hence a release of the armature, with the consequence that the critical range of the protective switchgear is thermally protected by means of the magnetic release trip. What must be considered to be a disadvantage in that overcurrent release device, which operates reliably on principle, is the fact that the manufacture of its part requires an extraordinarily high precision which cannot be easily achieved with simple means in series production.